When test cycles are first activated, there is both a predetermined budget and testing duration. Test cycles can become automatically locked when the budget has been depleted, or when the testing duration expires ("End Date"). Additionally, they may become locked if customers need to change requirements or add additional information. Testers may not submit any bugs or test cases for locked test cycles.
Remember, test cycles may lock well before the stated "End Date" listed in the platform. The various reasons for this include the customer temporarily locking to adjust the scope and instructions, the test cycle had a high participation rate that resulted in the bug limit being reached early, just to name a few. Therefore, if you're able to participate in a test cycle, please do so as early as possible, submitting in-scope findings sooner rather than later. When a test cycle locks, it may not reactivate again, so do not count on submitting any bugs unless the customer or project manager mentions otherwise in the Discussion Thread.